Slurry bubble column reactors are well known in the art and widely used as reactors for Low Temperature Fisher-Tropsch (LTFT) processes. LTFT processes include the step of bubbling synthesis gas, consisting mainly of carbon monoxide and hydrogen, through a column of hydrocarbon liquid wherein catalyst particles are suspended. The synthesis gas reacts in the presence of the catalyst to form predominantly liquid hydrocarbons. The liquid hydrocarbons are separated from the column, normally by filtration. The filters are preferably inside the column. The catalyst particle size distribution and filter mesh size is normally within a selected range. Typically such filters are manufactured from stainless steel woven wire mesh, sintered metal, wedge wire or ceramic filter elements. Often filter cake builds up on the outside of the filter, although this is normal and in some cases necessary for filtration; the filter cake needs to be removed when the filtration rate decreases below an acceptable level. The preferred way of removing this filter cake is periodic backflushing of the filter. However, catalyst fines may be trapped in the filter openings or collected on the filtrate side of the filter, and eventually, despite backflushing, the filtration rate may decrease below acceptable levels. Backflushing can in some instances compound the problem of decreasing filtration rates by forcing fines collected on the filtrate side of the filter back into the filter pores where the fines can get permanently trapped. It is well known that an acceptable filtration rate of liquids combined with acceptable loss of from such a LTFT column is a major engineering obstacle to be overcome for commercial success.
One solution to this problem offered in the prior art is a carefully selected catalyst particle size distribution and filter mesh size combination, as teached in WO00/45948. However, catalyst attrition occurs in a slurry bubble column reactor, and over time catalyst fines outside the selected range are formed inside the column. As a result a lot of research has focused on attrition resistant LTFT catalysts, without much success due to high flow velocities inside a slurry bubble column reactor. Another solution; teached in EP 609 079 is backflushing of the filter followed by a waiting period before filtration resumes, to allow the turbulence inside the column to break up the filter cake, and to remove the filter cake from the filter. However, catalyst fines inside the filter pores and on the filtrate side of the filter remain trapped.
It is envisaged that the invention can be applied in any method and apparatus for the separation of liquids from a three phase mixture.